Consumers are taking a strong interest in food labeling regulations and systems against a backdrop of concerns about safety and security of food. The labeling of food has become essential in terms of allowing consumers to evaluate and select food quality themselves. Wheat is converted into a variety of products through various processes and is also distributed in the marketplace. The labeling for macaroni, which is a typical product, is established by the Labeling Standards for Processed Food Quality and the Labeling Standards for Macaroni Quality, and “durum wheat semolina”, “durum wheat flour”, “strong wheat farina”, and “strong wheat flour” are displayed in descending order of content for the raw wheat flours used. Excluding tracking surveys for production processes, no technology exist that is capable of qualitatively and/or quantitatively discriminating common wheat from durum wheat in such processed wheat foods, and there is demand for the development of such technology.
To date, methods have been formulated for the specific and highly sensitive detection of wheat using various technologies. These methods can basically be classified into methods that use wheat-derived protein or DNA in the sample of interest as the detection target.
The methods for the detection of protein can be exemplified by electrophoretic methods, western blotting methods, and immunochemical methods, and by methods that are combinations of the preceding. In particular, ELISA methods have enjoyed broad commercial acceptance due to the availability of the peripheral equipment and reagents.
However, the ancestries of common wheat and durum wheat share a very strong commonality and their respective constituent components are thus also quite similar. The protein is no exception here, and while there are differences in the protein component ratios, there are almost no differences in the types of proteins present in these wheats. It is thus quite difficult to discriminate between common wheat and durum wheat using protein levels.
On the other hand, several technologies have also been devised for the specific detection of wheat using PCR, which is a gene amplification technology. However, the analysis of wheat DNA or genes is not always entirely adequate and this has made the development of an optimal testing method quite problematic.
Non-Patent Document 1 reports a wheat detection method that employs PCR and that targets the Wx-D1 gene encoded in the wheat D genome. This test method is capable of the very high-specificity detection of common wheat and is optimal for testing processed wheat products such as plant, grain, and wheat flours. Durum wheat, which lacks the D genome, is not detected by this test method.
Patent Document 1, on the other hand, discloses a PCR-based method that qualitatively and/or quantitatively detects wheat and that targets the starch synthase II (SSII) gene encoded in the wheat A, B, and D genomes. This detection method targets a common region of SSII A, B, and D and is capable of the specific and highly sensitive detection of wheat. A primer set that specifically discriminates SSII-D is disclosed in Patent Document 1, but the specificity is not necessarily assured and it is also unsuitable for quantitative measurements.
Non-Patent Document 2 reports that the starting genome undergoes physical cleavage in food processing steps at medium or high intensity, such as heating. When the PCR amplification target region in the wheat genome is long, the occurrence of cleavage therewithin brought about by the processing step may prevent the value measured by quantitative PCR from expressing the actual wheat content. As a result, a strategy must be devised for reducing the likelihood that the PCR target region will undergo fragmentation even when the wheat genome has been subject to fragmentation due to the application thereto of medium- or high-intensity processing.
Accordingly, there is desire for a method capable of the highly specific and highly sensitive detection of common wheat in a food raw material or a processed food product. In addition, since a suitable method does not yet exist for qualitatively and/or quantitatively discriminating between and detecting common wheat and a non-common wheat, for example, durum wheat, in a food raw material or a processed food, there is demand for the development of such a detection method.    Patent Document 1: Japanese Patent Application Laid-open No. 2009-5588    Non-Patent Document 1: Iida, M. et al., Development of taxon-specific sequences of common wheat for the detection of genetically modified wheat. J. Agric. Food Chem., 2005 Aug. 10; 53(16):6294-300.    Non-Patent Document 2: Yoshimura, T. et al., Comparative studies of the quantification of genetically modified organisms in foods processed from maize and soy using trial producing. J. Agric. Food Chem., 2005 Mar. 23; 53(6):2060-9.